1. Field of the Invention
The present invention relates to dielectric duplexers mainly for use in mobile communication, to radio frequency (RF) modules, and to communication apparatuses including the same.
2. Description of the Related Art
Referring to FIG. 7, the configuration of a known dielectric duplexer will now be described.
FIG. 7 is an external perspective view of a dielectric duplexer.
Referring to FIG. 7, the dielectric duplexer includes a dielectric block 51, inner-conductor-formed holes 52a to 52f, containing inner conductors 53a to 53f, an outer conductor 54, an input/output electrode 55, outer-conductorless portions 56 and 58, an antenna input/output electrode 57, and an inner-conductor-formed hole 59 functioning as an antenna excitation hole.
The substantially-rectangular-parallelepiped-shaped dielectric block 51 includes the inner-conductor-formed holes 52a to 52f, containing the inner conductors 53a to 53f, respectively. The outer conductor 54 is formed on the entirety of an exterior surface of the dielectric block 51. In the interior near an end face having first ends of the inner-conductor-formed holes 52a to 52f (the right back side in FIG. 7), inner-conductorless portions are provided to isolate the inner conductors 53a to 53f from the outer conductor 54, and hence the first ends become open-circuited ends. Second ends opposing the open-circuited ends (the left front side in FIG. 7) are short-circuited ends. As a result, dielectric resonators are formed. The inner-conductor-formed hole 59 is formed to penetrate the dielectric block 51 in the same axial direction as that of the inner-conductor-formed holes 52a to 52f. 
On the exterior surface of the dielectric block 51, the input/output terminal 55 extends from an end face in the direction in which the inner-conductor-formed holes 52a to 52f are arrayed to a mounting face (bottom face in FIG. 7) opposing a mounting board. The input/output terminal 55 is separated from the outer conductor 54 by the outer-conductorless portion 56 therebetween. Between the inner-conductor-formed holes 52c and 52d, the antenna input/output electrode 57 is formed to extend from the short-circuited end face having the short-circuited ends of the inner-conductor-formed holes 52a to 52f to the mounting face. The antenna input/output electrode 57 is separated from the outer conductor 54 by the outer-conductorless portion 58 therebetween. The antenna input/output electrode 57 is connected to an inner conductor in the inner-conductor-formed hole 59.
In this state, a first portion including the inner-conductor-formed holes 52a to 52c and a second portion including the inner-conductor-formed holes 52d to 52f each function as a three-stage band-pass-type dielectric filer in which the resonators formed by the inner conductors are coupled to one another. Thus, the dielectric duplexer having one of the filters as a transmitter filter and the other filter as a receiver filter is formed.
The above-described known dielectric duplexer has the following problems.
In the known dielectric duplexer, when the transmitter filter and the receiver filter are both band pass filters, the impedance in each of the pass bands of the transmitter filter and the receiver filter as seen from the antenna input/output electrode is substantially infinite. Thus, the transmitter filter and the receiver filter function as a dielectric duplexer.
FIG. 8 shows the equivalent circuit of a dielectric duplexer in which one of the filters is a band eliminate filter. In this case, as shown in FIG. 9, the impedance of the band eliminate filter in the pass band of the band pass filter is substantially zero.
FIG. 9 is a Smith chart showing the impedance of the transmitter filter (band eliminate filter) as seen from the antenna in the reception band (pass band) of the receiver filter (band pass filter). The Smith chart shows the impedance of a communication system in the 800 MHz band (the pass band of the receiver filter ranges from 810 MHz to 828 MHz), wherein symbol A indicates the impedance at 810 MHz and symbol B indicates the impedance at 828 MHz.
As shown in FIG. 9, the impedance of the transmitter filter as seen from the antenna is substantially zero, and hence the transmitter filter as seen from the antenna is essentially short-circuited in the reception band. This causes a reception signal from the antenna to enter the transmitter filter. As a result, the transmitter filter and the receiver filter do not function as a duplexer.
In order to solve this problem, a dielectric duplexer arranged as shown in FIGS. 10A to 10C is devised.
FIGS. 10A to 10C are three partial views of the dielectric duplexer, namely, FIGS. 10A and 10C illustrating faces having apertures of inner-conductor-formed holes and FIG. 10B illustrating the bottom face, which is a mounting face. FIGS. 10A to 10C show a band eliminate filter, which is one of the filters forming the dielectric duplexer.
Referring to FIGS. 10A to 10C, the dielectric duplexer includes a dielectric block 61, inner-conductor-formed holes 62a to 62d, 70, and 71, an outer conductor 64, outer-conductorless portions 66 and 68, an input/output electrode 67, and an antenna input/output electrode 69.
In the dielectric duplexer shown in FIGS. 10A to 10C, the inner-conductor-formed holes 62a to 62d, 70, and 71, containing inner conductors, are formed to extend from a first face of the dielectric block 61 (FIG. 10A) to a second face opposing the first face (FIG. 10C). The inner-conductor-formed holes 62a, 62c, 62d, 70, and 71 each have a stepped structure formed by portions having different internal diameters. The inner-conductor-formed hole 62b has a straight structure. The outer conductor 64 is formed on the substantial entirety of an exterior surface of the dielectric block 61. The outer-conductorless portions 66 and 68 are provided to extend from the first face (FIG. 10A) to the bottom face, which is the mounting face (FIG. 10B). This results in the formation of the input/output electrode 67 and the antenna input/output electrode 69. The inner-conductor-formed holes 70 and 71 are connected to the input/output electrode 67 and the antenna input/output electrode 69, respectively. An inner-conductorless portion is provided in the interior near the first face (FIG. 10A) including the input/output electrode 67 and the antenna input/output electrode 69, and hence an open-circuited end of a resonator formed by the inner-conductor-formed hole 62c is formed. Inner-conductorless portions are provided in the interior near the second face opposing the first face (FIG. 10C), and hence open-circuited ends of resonators formed by the inner-conductor-formed holes 62a and 62d are formed.
The inner-conductor-formed holes 62a to 62d, 70, and 71 are arranged in two lines from the bottom face to the top face of the dielectric block 61. The resonators formed by the inner-conductor-formed holes 62a, 70, 62c, and 62d form two one-stage band eliminate filters by interdigitally coupling the inner-conductor-formed hole 62a with the inner-conductor-formed hole 70 and by interdigitally coupling the inner-conductor-formed hole 62c with the inner-conductor-formed hole 62d. The one-stage band eliminate filters are interdigitally coupled to each other at an electrical angle of xcfx80/2 between the inner-conductor-formed hole 70 and the inner-conductor-formed hole 62d. As a result, a two-stage band eliminate filter is formed.
The resonator formed by the inner-conductor-formed hole 71 functions as a xcfx80/2 phase circuit by interdigitally coupling to the resonator formed by the inner-conductor-formed hole 62d at an electrical angle of xcfx80/2. The band eliminated by the band eliminate filter, as seen from the antenna input/output electrode 69, i.e., the impedance of the band eliminate filter in the pass band of the band pass filter, can be increased to be substantially infinite. As a result, the filter functions as a duplexer.
This arrangement causes the following problem. Specifically, the interdigital coupling of the resonator formed by the inner-conductor-formed hole 62d with three resonators formed by the inner-conductor-formed holes 62c, 70, and 71 requires the inner-conductor-formed holes to be arranged at two stages at different heights. This results in an increase in the height of the dielectric block 61.
Compared with the one-stage structure, the two-stage structure can only allow smaller space in the height direction per resonator. This causes deterioration of the unloaded Q factor and an increase in the insertion loss.
The phase width in the reception band (the pass band of the band pass filter) changes as shown in FIG. 11.
The larger the number of resonators formed by the inner-conductor-formed holes forming the filters, the larger the number of devices having frequency characteristics.
FIG. 11 is a Smith chart showing the impedance of the transmitter filter in the reception band as seen from the antenna input/output electrode. The Smith chart shows the impedance of a communication system in the 800 MHz band (the pass band of the receiver filter ranges from 810 MHz to 828 MHz), wherein symbol A indicates the impedance at 810 MHz and symbol B indicates the impedance at 828 MHz. As shown in FIG. 11, the phase width xcex8 is variable depending on the range of frequencies in the reception band. The receiver filter cannot have sufficient matching over the entire range of frequencies in the reception band, resulting in an increase in the insertion loss.
Also, the dielectric block increases in size. This increase causes an increase in material cost, leading to an increase in the overall cost.
Accordingly, it is an object of the present invention to provide a dielectric duplexer with a simple configuration, which includes a band eliminate filter as one of two filters and which can easily have matching with an antenna, and to provide a communication apparatus including the same.
According to an aspect of to the present invention, a dielectric duplexer is provided including a dielectric block including two filters, each filter including two input/output electrodes, one of which is an antenna input/output electrode. At least one of the filters is a band eliminate filter. The exterior of the dielectric block includes a phase circuit between the antenna input/output electrode of the band eliminate filter and an antenna. The phase is shifted by the phase circuit so that the antenna input/output electrode of the band eliminate filter, as seen from the antenna, is essentially open-circuited. Accordingly, a miniaturized dielectric duplexer having improved characteristics can be formed at low cost.
Of the two filters, one may be the band eliminate filter, and the other may be a band pass filter. The antenna may be connected to the antenna input/output electrode of the band pass filter.
The band eliminate filter forming the dielectric duplexer may be formed by a plurality of resonators, which are interdigitally coupled to one another. Accordingly, a filter with low loss can be formed, and a dielectric duplexer having improved characteristics can be formed.
The phase circuit and the dielectric block including a plurality of dielectric filters may be mounted on a single substrate. Accordingly, a dielectric duplexer can be formed by a simple configuration, and the degree of freedom in designing the dielectric duplexer can be enhanced.
According to another aspect of the present invention, a communication apparatus including the foregoing dielectric duplexer is provided. Accordingly, a communication apparatus having improved communication characteristics can be formed.